The present invention relates to a suppressing method of iso-citric acid formation in producing citric acid from hydrocarbons by fermentation.
It has been well known that citric acid is produced by the assimilation of normal paraffins as carbon source.
Furthermore, we, inventors, have proposed the production process of citric acid from normal .alpha.-olefins of C.sub.8-40 as carbon source by culturing the microorganisms selected from the group of Candida tropicalis, Candida intermedia and Candida brumptii and their mutants and their variants, in U.S. Pat. No. 4,180,626.
Iso-citric acid is commonly accumulated in the citric acid fermentation using hydrocarbons as carbon source. The yield of iso-citric acid accumulated in the culture medium is often equal to or higher than that of citric acid, though said yield is somewhat different by the kinds of microorganisms and the cultural conditions.
We have discovered that the iso-citric acid formation in the citric acid production from hydrocarbons by ferementation is suppressed by adding the specific non-ionic surface active agents, such as sorbitan fatty acid esters and polyoxy-ethylene sorbitan fatty acid esters to said culture medium.
In general, the steric isomers are often produced in organic acid fermentations. For suppressing the formation of isomer and dominating the normal compound, some mutants have been commonly used. However, said method requires a great deal of work and cost in search of the mutants and in examination of the cultural conditions.
In the present invention, the formation of iso-citric acid can be suppressed by adding the specific non-ionic surface active agent to the culture medium, and any mutant is not required. This effect has a great industrial significance.